Publication U.S. Pat. No. 5,434,500 makes known a magnetic field generator that includes a detector with a position indicator, with which the magnetic field generator serves as a sending unit that is placed on a first side of a wall at the point to be located and creates a magnetic field at this point. The associated detector serves as a receiving unit and is moved over the surface of the wall facing away from the sending unit. The receiving unit includes two pairs of two detectors each that measure the relative strength of the magnetic field. By measuring this relative strength of the magnetic field at each of the individual detectors, it is possible to locate the position of the magnetic field generator and/or the projection of this position on the side of the wall opposite from the generator. With the device described in U.S. Pat. No. 5,434,500, the strength of the detected magnetic field is visualized using an optical display. When the strength of the detected magnetic field is equal at all four detection elements, the receiving unit is located directly opposite the sending unit. A quantitative measurement of the wall thickness is not provided for with the device described in U.S. Pat. No. 5,434,500, however.
Publication DE 34 46 392 A1 makes known a method for identifying a test point on one side of a wall, from the other side of the wall. With this method, which is used with metallic walls of a container in particular, it is provided—in order to more quickly identify the test point and increase the accuracy of the position identification—that a magnetic pole is placed on the wall at the test point, and that the magnetic field of the magnetic pole penetrating the wall is detected on the opposite side of the wall from the magnetic pole. To detect the magnetic field, a Hall effect component is preferably used with the method described in DE 34 46 392 A1.
The devices known from the related art have the disadvantage, among others, that metallic parts in the material, e.g., a wall, ceiling or floor, such as steel girders or reinforcing rods, greatly interfere with the detection and can even render it impossible to carry out. In addition, the positioning accuracy of devices of this type tends to be poor.
The object of the present invention, therefore, is to provide a method and a device that allow material thickness to be determined quickly, reliably and precisely.
The object is attained according to the present invention by a method having the features of Claim 1. The object is also attained by a device having the features of Claim 9.